Semiconductor switch

ABSTRACT

A semiconductor switch includes four diodes, two transistors, and a capacitor. The capacitor includes a fourth terminal and a fifth terminal. An anode of a third diode is connected to a third terminal of a first transistor. A cathode of the third diode is connected to a first terminal of the first transistor and to an anode of a first diode. An anode of a fourth diode is connected to a third terminal of a second transistor. A cathode of the fourth diode is connected to a first terminal of the second transistor and to an anode of the second diode. A cathode of the first diode is connected to a cathode of the second diode and to the fourth terminal of the capacitor. An anode of the third diode is connected to the anode of the fourth diode and to the fifth terminal of the capacitor.

BACKGROUND

With the growth of wind energy systems, solar power systems, electricvehicles and electric storage systems, the electric grid is expected tosee a major transformation. In realizing this transformation, thereliability, stability, and efficiency of the grid will require powerflow controllers with flexible and higher performance levels than stateof the art devices based on mechanical switches.

Four-quadrant (4-quadrant) switches for alternating current (AC) powerconversion applications typically use single-quadrant semiconductorslike metal oxide semiconductor field effect transistors (MOSFETs) andinsulated-gate bipolar transistors (IGBTs) along with diodes, which posea persistent problem. For example, a classical topology of using asingle-quadrant switch across direct current (DC) terminals of a fullbridge rectifier results in excessive conduction losses due to threesemiconductors in a current conduction path. A better realization usestwo series-connected single-quadrant switches, each with anantiparallel-diode resulting in reduced conduction losses; however, thetwo series-connected single-quadrant switches require careful sequencingof commutation to prevent voltage and/or current overshoots duringswitching. Additionally, the voltage blocking capability of discretedevices places an upper bound on the power for high voltageapplications. These issues pose a significant barrier to commercialapplication of matrix converters, AC to AC converters, and solid statecircuit breakers for AC systems that require practical, simple, andreliable semiconductor switches that are capable of 4-quadrant operationfor conducting currents in both directions while blocking voltage inboth directions.

SUMMARY

In an example embodiment, a semiconductor switch is provided that mayinclude, but is not limited to, a first diode, a second diode, a thirddiode, a fourth diode, a first transistor, a second transistor, and acapacitor. The first diode includes, but is not limited to, a firstanode and a first cathode. The second diode includes, but is not limitedto, a second anode and a second cathode. The third diode includes, butis not limited to, a third anode and a third cathode. The fourth diodeincludes, but is not limited to, a fourth anode and a fourth cathode.The first transistor includes, but is not limited to, a first terminal,a second terminal, and a third terminal. The second transistor includes,but is not limited to, a fourth terminal, a fifth terminal, and a sixthterminal. The capacitor includes, but is not limited to, a seventhterminal and an eighth terminal. The third anode of the third diode isconnected to the third terminal of the first transistor, and the thirdcathode of the third diode is connected to the first terminal of thefirst transistor and to the first anode of the first diode. The fourthanode of the fourth diode is connected to the third terminal of thesecond transistor, and the fourth cathode of the fourth diode isconnected to the first terminal of the second transistor and to thesecond anode of the second diode. The first cathode of the first diodeis connected to the second cathode of the second diode and to theseventh terminal of the capacitor. The third anode of the third diode isconnected to the fourth anode of the fourth diode and to the eighthterminal of the capacitor opposite the seventh terminal of thecapacitor.

In another example embodiment, a power conversion system is provided.The power conversion system includes, but is not limited to, analternating current (AC) electrical source, an AC electrical loadcircuit, and the semiconductor switch connected between the electricalsource and the electrical load circuit.

Other principal features of the disclosed subject matter will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the disclosed subject matter will hereafterbe described referring to the accompanying drawings, wherein likenumerals denote like elements.

FIG. 1 is a circuit diagram of a semiconductor switch in accordance withan illustrative embodiment.

FIG. 2 is a circuit diagram for modeling the semiconductor switch ofFIG. 1 in an on-state in accordance with an illustrative embodiment.

FIG. 3 is a circuit diagram for modeling the semiconductor switch ofFIG. 1 in an off-state in accordance with an illustrative embodiment.

FIG. 4 is a circuit diagram for modeling the semiconductor switch ofFIG. 1 connected between an alternating current (AC) electrical sourceand an AC electrical load in accordance with an illustrative embodiment.

FIG. 5 shows a simulated load voltage generated using the semiconductorswitch of FIG. 1 as a pulse width modulated (PWM) resistive chopper inaccordance with an illustrative embodiment.

FIG. 6 shows a measured load voltage generated using the semiconductorswitch of FIG. 1 as the PWM resistive chopper in accordance with anillustrative embodiment.

FIG. 7 is a circuit diagram of two series connected semiconductorswitches of FIG. 1 connected between the AC electrical source and the ACelectrical load in accordance with an illustrative embodiment.

FIG. 8 shows a simulated voltage generated by a first semiconductorswitch of the two series connected semiconductor switches of FIG. 7 inaccordance with an illustrative embodiment.

FIG. 9 shows a simulated voltage generated by a second semiconductorswitch of the two series connected semiconductor switches of FIG. 7 inaccordance with an illustrative embodiment.

FIG. 10 is a circuit diagram of a first semiconductor switch of FIG. 1connected between a first AC electrical source and the AC electricalload and of a second semiconductor switch of FIG. 1 connected between asecond AC electrical source and the AC electrical load in accordancewith an illustrative embodiment.

FIG. 11 is a circuit diagram of a first semiconductor switch of FIG. 1and of a second semiconductor switch of FIG. 1 connected to form anAC-AC buck converter in accordance with an illustrative embodiment.

FIG. 12 shows a simulated source voltage provided to the AC-AC buckconverter of FIG. 11 in accordance with an illustrative embodiment.

FIG. 13 shows a simulated load voltage generated from the AC-AC buckconverter of FIG. 11 in accordance with an illustrative embodiment.

FIG. 14 is a circuit diagram of a first semiconductor switch of FIG. 1connected to form an AC circuit breaker in accordance with anillustrative embodiment.

FIG. 15 shows a simulated source current provided to the AC circuitbreaker of FIG. 14 in accordance with an illustrative embodiment.

FIG. 16 shows the simulated source current provided to the AC circuitbreaker of FIG. 14 zoomed to a time period when a fault condition occursin accordance with an illustrative embodiment.

FIG. 17 is a block diagram of a power conversion system in accordancewith an illustrative embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a semiconductor switch 100 is shown in accordancewith an illustrative embodiment. Semiconductor switch 100 may beconnected between a source terminal 102 and a load terminal 104.Semiconductor switch 100 may include a first diode 122, a second diode132, a third diode 124, a fourth diode 134, a first transistor 126, asecond transistor 136, and a capacitor 130. Third diode 124 is connectedantiparallel across first transistor 126, and fourth diode 134 isconnected antiparallel across second transistor 136.

First diode 122, second diode 132, third diode 124, and fourth diode 134may be diodes of various types such as a p-n junction type, a thyristor,etc. with various ratings. As understood by a person of skill in theart, a diode is a two-terminal electronic component that conductscurrent primarily in one direction from an anode to a cathode.

First transistor 126 may include a first terminal 127, a second terminal128, and a third terminal 129. First terminal 127, second terminal 128,and third terminal 129 may be referred to as a drain, a gate, and asource, respectively, for a metal-oxide-semiconductor field-effecttransistor (MOSFET), or as a collector, a gate, and an emitter,respectively, for an insulated-gate bipolar transistor (IGBT), or as acollector, a base, and an emitter, respectively, for a bipolar junctiontransistor (BJT).

Second transistor 136 may include a fourth terminal 137, a fifthterminal 138, and a sixth terminal 139. Fourth terminal 137, fifthterminal 138, a sixth terminal 139 may be referred to as a drain, agate, and a source, respectively, for a MOSFET, or as a collector, agate, and an emitter, respectively, for an IGBT, or as a collector, abase, and an emitter, respectively, for a BJT. Depending on a switchinglogic and whether first transistor 126 and second transistor 136 are ann-type or a p-type, the drain and the source may be reversed. A voltageapplied to second terminal 128 and to fifth terminal 138 determines aswitching state of first transistor 126 and of second transistor 136,respectively, as in an on-state or as an in an off-state. Firsttransistor 126 and second transistor 136 are switched into the on-stateor the off-state at the approximately the same time such that each iseither in the on-state or in the off-state at the same time. Firsttransistor 126 and second transistor 136 have a same rating and a sametransistor type. In the illustrative embodiment, first transistor 126and second transistor 136 are n-type, enhancement mode MOSFETs formed ofvarious materials though other transistor types may be used.

A source line 106 connects to a source connector 144 between a firstanode of first diode 122 and a third cathode of third diode 124 andfirst terminal 127 of first transistor 126. A load line 116 connects toa load connector 146 between a second anode of second diode 132 and afourth cathode of fourth diode 134 and fourth terminal 137 of secondtransistor 136. Source line 106 may split into a first line 108 and asecond line 110. First line 108 connects source line 106 to the firstanode of first diode 122. Second line 110 connects source line 106 tothe third cathode of third diode 124 and to first terminal 127 of firsttransistor 126. Load line 116 may split into a third line 118 and afourth line 120. Third line 118 connects load line 116 to the secondanode of second diode 132. Fourth line 120 connects load line 116 to thefourth cathode of fourth diode 134 and to first terminal 137 of secondtransistor 136. A fifth line 112 connects between a first cathode offirst diode 122 and a second cathode of second diode 132. A sixth line114 connects between a third anode of third diode 124 and a fourth anodeof fourth diode 134 and also between third terminal 129 of firsttransistor 126 and sixth terminal 139 of second transistor 136. Fifthline 112 may be referred to as a positive bus of semiconductor switch100, and sixth line 114 may be referred to as a negative bus ofsemiconductor switch 100.

Capacitor 130 connects between fifth line 112 and sixth line 114.Capacitor 130 may be a capacitor of various types and with variousratings. As understood by a person of skill in the art, a capacitor is apassive two-terminal electronic component that stores electrical energyin an electric field and has an associated rated capacitance value C. Asa result, capacitor 130 may include a seventh terminal 140 and an eighthterminal 142. In an illustrative embodiment, seventh terminal 140 may bereferred to as a positive terminal of capacitor 130, and eighth terminal142 may be referred to as a negative terminal of capacitor 130.

Semiconductor switch 100 can be described as a bidirectional voltage anda bidirectional current H-bridge module formed using two unidirectionalvoltage bidirectional current semi-controlled half-bridge modules thateach consist of two diodes and a transistor. Capacitor 130 is connectedin parallel between the two semi-controlled half-bridge modules. Firstdiode 122, third diode 124 and first transistor 126 form a firsthalf-bridge module, and second diode 132, fourth diode 134 and secondtransistor 136 form a second half-bridge module.

Referring to FIG. 2, a circuit diagram for modeling the semiconductorswitch of FIG. 1 in an on-state is shown in accordance with anillustrative embodiment. Referring to FIG. 3, a circuit diagram formodeling the semiconductor switch of FIG. 1 in an off-state is shown inaccordance with an illustrative embodiment. Though an ideal capacitordoes not dissipate energy, capacitor 130 generally has a leakage currentthat can be modeled as a resistor 200 connected between fifth line 112and sixth line 114 and having a resistance value R.

For the off-state of semiconductor switch 100, first transistor 126 andsecond transistor 136 are maintained in an off-state based on anoff-state control signal provided by a controller 1702 (shown referringto FIG. 17) to second terminal 128 of first transistor 126 and to fifthterminal 138 of second transistor 136. For the on-state of semiconductorswitch 100, first transistor 126 and second transistor 136 are turned onbased on an on-state control signal provided by controller 1702 tosecond terminal 128 of first transistor 126 and to fifth terminal 138 ofsecond transistor 136.

As shown referring to FIG. 3, during the off-state, both firsttransistor 126 and second transistor 136 are switched off, and firstdiode 122, second diode 132, third diode 124, and fourth diode 134behave as a full-wave rectifier, and charge capacitor 130 to a peakvalue of an AC voltage (V) after which first diode 122, second diode132, third diode 124, and fourth diode 134 stop conducting. Each offirst diode 122, second diode 132, third diode 124, and fourth diode 134are reverse biased and ensure that there is no current flow in the ACcircuit.

On the other hand, as shown referring to FIG. 2, during the on-state,both first transistor 126 and second transistor 136 are switched on toprovide a current flow path for a current that bypasses capacitor 130.If the current is positive and flows from source terminal 102 towardload terminal 104, first transistor 126 and fourth diode 134 provide acurrent flow path. If the current is negative and flows from loadterminal 104 toward source terminal 102, second transistor 136 and thirddiode 124 provide a current flow path. As a result, bidirectionalcurrent flow is provided.

A primary operating principle of semiconductor switch 100 is thefundamental direct current (DC) blocking property of capacitor 130 thatacts as an open circuit for steady state DC currents because anycapacitor appears as an open circuit in a DC path of currents. Thus,semiconductor switch 100 with capacitor 130 across DC terminals definedbetween fifth line 112 and sixth line 114 appears to be an open circuitacross the AC terminals of source terminal 102 and load terminal 104 atsteady state regardless of a polarity of the AC voltage. A steady statecondition for semiconductor switch 100 is reached after capacitor 130has reached its DC bias level (typically drawing energy from the ACcircuit) that prevents any further current conduction. Semiconductorswitch 100 is shoot-through proof because there is no totem-poleconnected half-bridge in the circuit topology.

Design of power circuit components for semiconductor switch 100 may bebased on two major application areas that relate to a rate of switchingbetween the on-state and the off-state of first transistor 126 andsecond transistor 136, and thus, switching of semiconductor switch 100between the on-state and the off-state. A bias voltage for capacitor 130may be selected as an adequate level to accommodate any leakage and lossof energy due to resistor 200 modeled across capacitor 130 during anon-state so that semiconductor switch 100 operates as an open circuitduring its off-state. Referring to FIG. 2, if a leakage of capacitorenergy can be modeled in terms of resistor 200 having a resistance valueR and capacitor 130 having the capacitance value C, a time constant RCmay be selected to be much larger than an expected interval betweensuccessive off-states of semiconductor switch 100 to ensure thatcapacitor 130 can provide an acceptable blocking condition when firsttransistor 126 and second transistor 136 are switched to the off-state.

For applications of semiconductor switch 100 in power converters thatoperate at several kilohertz (kHz) to several 100 s of kHz, capacitor130 may be implemented using a film capacitor having a capacitance valueC of a fraction of a microfarad (μF) with a resistance value R in therange of 100 kiloohms (kΩ) that provide an adequately large timeconstant RC compared to an on-state interval of semiconductor switch100.

For applications of semiconductor switch 100 in general purpose powercircuit switching applications such as solid state relays, circuitbreakers, etc., a rate of switching may be event-driven or occasionalsuch that a time interval between switching events may range fromminutes to days. Here a much larger capacitance value C may be selectedto provide an adequate amount of energy storage. As another option, oneor both of first transistor 126 and second transistor 136 can be turnedoff for a short interval of time to recharge capacitor 130 bycirculating the load current through capacitor 130 without anyappreciable impact on the load. A separate bias circuit (not shown) mayalso be used to pre-charge capacitor 130 with a DC voltage that isgreater than or equal to a peak value of the AC blocking voltage.

The current ratings of first transistor 126 and second transistor 136and of third diode 124 and fourth diode 134 may be selected to carry theload current based on the application area. A rating of first transistor126 and third diode 124 may be selected to carry a positive half-cycleof the current and a rating of second transistor 136 and fourth diode134 may be selected to carry a negative half-cycle of the current. Arating of first diode 122 and second diode 132 may be selected to carryonly the leakage current used to maintain the DC bias conditions forcapacitor 130.

Referring to FIG. 4, an illustrative application of semiconductor switch100 is shown in accordance with an illustrative embodiment.Semiconductor switch 100 is connected between an alternating current(AC) electrical source 400 through source terminal 102 and an ACelectrical load 402 through load terminal 104. AC electrical source 400may include one or more AC source circuits that provide electricalpower. AC electrical load 402 may include one or more AC load circuitsthat act as electrical loads that receive the provided electrical power.Some or all of AC electrical source 400 and/or AC electrical load 402may provide bidirectional power flow such that a source circuit and/or aload circuit may act as a power source during a first time period and asan electrical load during a second time period. As discussed previously,semiconductor switch 100 provides bidirectional current flow between ACelectrical source 400 and AC electrical load 402 while blocking voltagefrom AC electrical load 402 to AC electrical source 400 under control ofa switching state of semiconductor switch 100 by controller 1702.

Referring to FIG. 5, a simulated load voltage curve 500 generated usingsemiconductor switch 100 as a pulse width modulated (PWM) resistivechopper is shown in accordance with an illustrative embodiment.Referring to FIG. 6, a measured load voltage curve 600 generated using ahardware implementation of semiconductor switch 100 as the PWM resistivechopper is shown in accordance with an illustrative embodiment. ACelectrical source 400 was implemented as a 12 volt (V) 60 hertz (Hz) ACsource and AC electrical load 402 was implemented as a 60 watt (W) lampresistive load. A capacitance value for capacitor 130 was 220 μF with aresistance value of 100 kΩ. Semiconductor switch 100 was operated using500 Hz switching frequency with a duty ratio of approximately 66%. Therelatively low 500 Hz switching frequency was selected so that theswitching phenomenon could be clearly visualized in the results of FIGS.5 and 6. First transistor 126 and second transistor 136 were implementedas MOSFETs. Capacitor 130 was used to pulse width modulate the ACvoltage so that only a fraction of the AC voltage was applied to ACelectrical load 402.

Referring to FIG. 5, non-zero intervals of simulated load voltage curve500 during a positive half-cycle 502 were generated with both firsttransistor 126 and second transistor 136 switched to the on-state andwith current flowing from source terminal 102 toward load terminal 104through first transistor 126 and fourth diode 134. Non-zero intervals ofsimulated load voltage curve 500 during a negative half-cycle 504 weregenerated with both first transistor 126 and second transistor 136switched to the on-state and with current flowing from load terminal 104toward source terminal 102 through second transistor 136 and third diode124. A width 506 of each zero-interval is an inverse of the 500 Hzswitching frequency. As a result, width 506 of each zero-interval can beshortened by increasing the switching frequency.

Similarly, referring to FIG. 6, non-zero intervals of measured loadvoltage curve 600 during a positive half-cycle 602 were generated withboth first transistor 126 and second transistor 136 switched to theon-state and with current flowing from source terminal 102 toward loadterminal 104 through first transistor 126 and fourth diode 134. Non-zerointervals of measured load voltage curve 600 during a negativehalf-cycle 604 were generated with both first transistor 126 and secondtransistor 136 switched to the on-state and with current flowing fromload terminal 104 toward source terminal 102 through second transistor136 and third diode 124. A width 606 of each zero-interval is theinverse of the 500 Hz switching frequency. As a result, bidirectionalcurrent flow and unidirectional voltage with voltage blocking isprovided by semiconductor switch 100.

In alternative embodiments, any number of semiconductor switches 100 maybe connected in series between AC electrical source 400 and ACelectrical load 402. For example, referring to FIG. 7, a circuit diagramof two series connected semiconductor switches 700 connected between ACelectrical source 400 and AC electrical load 402 are shown in accordancewith an illustrative embodiment. The two series connected semiconductorswitches 700 include a first semiconductor switch 100 a and a secondsemiconductor switch 100 b that are both implementations ofsemiconductor switch 100.

First semiconductor switch 100 a may include a first diode 122 a, asecond diode 132 a, a third diode 124 a, a fourth diode 134 a, a firsttransistor 126 a, a second transistor 136 a, and a capacitor 130 a.Second semiconductor switch 100 b may include a first diode 122 b, asecond diode 132 b, a third diode 124 b, a fourth diode 134 b, a firsttransistor 126 b, a second transistor 136 b, and a capacitor 130 b.

Source line 106 connects to a source connector 144 a of firstsemiconductor switch 100 a between a first anode of first diode 122 aand a third cathode of third diode 124 a and a first transistor 126 a.Load line 116 connects to a load connector 146 b of second semiconductorswitch 100 b between a second anode of second diode 132 b and a fourthcathode of fourth diode 134 b and second transistor 136. Source line 106may split into a first line 108 a and a second line 110 a. Load line 116may split into a third line 118 b and a fourth line 120 b. A seventhline 702 connects between a load connector 146 a of first semiconductorswitch 100 a and a source connector 144 b of second semiconductor switch100 b to connect first semiconductor switch 100 a and a secondsemiconductor switch 100 b in series between AC electrical source 400and AC electrical load 402.

Series connection of a plurality of semiconductor switches 100 enables ahigher voltage blocking capability because the peak AC line voltage issplit between the series connected switches. First transistor 126 andsecond transistor 136 of each semiconductor switch 100 (e.g., firsttransistor 126 a and second transistor 136 a of first semiconductorswitch 100 a and first transistor 126 b and second transistor 136 b ofsecond semiconductor switch 100 b) can be switched to the on-state andoff-state independently and with a small time delay between them withoutcausing issues with circuit operation. A small bleeding or equalizationcapacitor can be connected in parallel with capacitor 130 a of firstsemiconductor switch 100 a and with capacitor 130 b of secondsemiconductor switch 100 b to ensure adequate voltage balancing withoutactive control.

Referring to FIG. 8, a first simulated voltage curve 800 generated byfirst semiconductor switch 100 a of the two series connectedsemiconductor switches 700 is shown in accordance with an illustrativeembodiment. Referring to FIG. 9, a second simulated voltage curve 900generated by second semiconductor switch 100 b of the two seriesconnected semiconductor switches 700 is shown in accordance with anillustrative embodiment. Both first simulated voltage curve 800 andsecond simulated voltage curve 900 have similar characteristics tosimulated load voltage curve 500. First simulated voltage curve 800 andsecond simulated voltage curve 900 were generated using semiconductorswitch 100 implemented similar to that described with reference to FIG.5 except using a duty ratio of approximately 50%. The equal division ofthe AC source voltage between first semiconductor switch 100 a andsecond semiconductor switch 100 b is clearly shown. The modularrealization of semiconductor switch 100 makes it essentially insensitiveto small variations in switching time delays and circuit parametervalues by using a blocking capacitance value C for capacitor 130 in eachsemiconductor switch 100.

Semiconductor switch 100 can also be connected between a plurality of ACelectrical loads 402 and a plurality of AC electrical sources 400 witheach semiconductor switch 100 acting as a throw or a pole of multiplethrows and multiple poles to realize particular power flow controlrequirements. For example, referring to FIG. 10, a single pole, doublethrow switching arrangement 1000 is shown in accordance with anillustrative embodiment. Single pole double throw switching arrangement1000 may include first semiconductor switch 100 a and secondsemiconductor switch 100 b connected in parallel. First semiconductorswitch 100 a is connected between a first AC electrical source 400 a andAC electrical load 402, and second semiconductor switch 100 b isconnected between a second AC electrical source 400 b and AC electricalload 402.

A first source line 106 a from first AC electrical source 400 a connectsto source connector 144 a of first semiconductor switch 100 a. A firstload line 116 a connects between load connector 146 a of firstsemiconductor switch 100 a and load line 116 of AC electrical load 402.A second source line 106 b from second AC electrical source 400 bconnects to source connector 144 b of second semiconductor switch 100 b.A second load line 116 b connects between load connector 146 b of secondsemiconductor switch 100 b and load line 116 of AC electrical load 402.

Any number of semiconductor switches can be connected in parallelbetween different AC electric sources and AC electrical loads 402.Similarly, multiple poles may be implemented using a plurality of ACelectrical loads 402. Additionally, parallel connected semiconductorswitch 100 may include one or more series connected semiconductorswitches 100 in a manner similar to the two series connectedsemiconductor switches 700 to provide a higher voltage blockingcapability.

Operation of parallel connected first semiconductor switch 100 a andsecond semiconductor switch 100 b may be used to direct power flow fromfirst AC electrical source 400 a and from second AC electrical source400 b to AC electrical load 402. Controller 1702 may control an on-stateand an off-state of first semiconductor switch 100 a and secondsemiconductor switch 100 b to achieve the particular power flow controlrequirements from first AC electrical source 400 a to AC electrical load402 and from second AC electrical source 400 b to AC electrical load402. Controller 1702 further may control an on-state and an off-state ofeach parallel connected semiconductor switch 100 to achieve theparticular power flow control requirements from one or more AC electricsources and one or more AC electric loads.

Referring to FIG. 11, a circuit diagram of first semiconductor switch100 a and of second semiconductor switch 100 b connected to form anAC-AC buck converter 1100 is shown in accordance with an illustrativeembodiment. AC-AC buck converter 1100 may include first semiconductorswitch 100 a, second semiconductor switch 100 b, an inductor 1102 and asecond capacitor 1104 connected between AC electrical source 400 and ACelectrical load 402. Inductor 1102 may include a ninth terminal 1110 anda tenth terminal 1112. Second capacitor 1104 may include an eleventhterminal 1114 and a twelfth terminal 1116.

First semiconductor switch 100 a is connected between AC electricalsource 400 and both second semiconductor switch 100 b and ninth terminal1114 of inductor 1102. Source line 106 connects to source connector 144a of first semiconductor switch 100 a. Second semiconductor switch 100 bis connected between both first semiconductor switch 100 a and ninthterminal 1114 of inductor 1102 and an eighth line 1108 that may bereferred to as a negative bus between AC electrical source 400 and ACelectrical load 402. Second load line 116 b out of second semiconductorswitch 100 b connects to load connector 146 b of second semiconductorswitch 100 b and eighth line 1108. Second capacitor 1104 is connectedbetween load line 116 and eighth line 1108 in parallel with ACelectrical load 402.

Ninth terminal 1110 of inductor 1102 is connected between load connector146 a of first semiconductor switch 100 a and source connector 144 b ofsecond semiconductor switch 100 b. A load line 116 a out of firstsemiconductor switch 100 a connects to source line 106 b into secondsemiconductor switch 100 b. Tenth terminal 1112 of inductor 1102 isconnected between eleventh terminal 1114 of second capacitor 1104 and ACelectrical load 402. A ninth line 1106 connects ninth terminal 1110 ofinductor 1102 between first load line 116 a out of first semiconductorswitch 100 a and second source line 106 b into second semiconductorswitch 100 b.

Referring to FIG. 12, a simulated source voltage 1200 provided to theAC-AC buck converter 1100 is shown in accordance with an illustrativeembodiment. Referring to FIG. 13, a simulated load voltage 1300generated from the AC-AC buck converter 1100 is shown in accordance withan illustrative embodiment. First semiconductor switch 100 a and secondsemiconductor switch 100 b are used as complimentary switches. A PWMoutput is interfaced to AC electrical load 402 through an L-C filterdefined by inductor 1102 and second capacitor 1104 with an inductancevalue L of inductor 1102 and a second capacitance value C₂ of secondcapacitor 1104 chosen to provide a selected ripple reduction. Firstsemiconductor switch 100 a and second semiconductor switch 100 b wereoperated to step down a voltage of AC electrical source 400, as shown inFIG. 12, by 50% to AC electrical load 402 as shown in FIG. 13. A similarapproach can be used to implement any AC power converter including aboost converter, a buck-boost converter, a matrix converter, etc. thoughone or more semiconductor switches may be arranged in various mannersand possibly with other circuit elements depending on a type ofconverter and/or other circuit elements with which the one or moresemiconductor switches are integrated. A design of the L-C filter issimilar to that corresponding to DC to DC converters and may be governedprimarily by the switching frequency to select the inductance value L ofinductor 1102 and the second capacitance value C₂ of second capacitor1104.

Referring to FIG. 14, a circuit diagram of semiconductor switch 100connected to form an AC circuit breaker is shown in accordance with anillustrative embodiment. In the illustrative embodiment, semiconductorswitch 100 configured to operate as an AC circuit breaker may includefirst diode 122 implemented as a thyristor or a silicone-controlledresistor (SCR) with a first control gate 1400, and second diode 132implemented as a thyristor or an SCR with a second control gate 1402.Under normal on-conditions, first diode 122, second diode 132, firsttransistor 126, and second transistor 136 are switched to an on-state bycontroller 1702 using first control gate 1400 of first diode 122, secondcontrol gate 1402 of second diode 132, second terminal 128 of firsttransistor 126, and fifth terminal 138 of second transistor 136,respectively.

When an over-current, short circuit or any undesirable condition isdetected, first diode 122, second diode 132, first transistor 126, andsecond transistor 136 are switched to an off-state by controller 1702using first control gate 1400 of first diode 122, second control gate1402 of second diode 132, second terminal 128 of first transistor 126,and fifth terminal 138 of second transistor 136, respectively. At theinstant of turn-off, the current through one of first transistor 126 orsecond transistor 136 is immediately transferred to one of first diode122 or of second diode 132, respectively, depending on a polarity of thecurrent. The current flows through capacitor 130 charging it furtheruntil the current reaches zero at which point first diode 122 or seconddiode 132 stop conducting, and the AC circuit breaker is in itsoff-state. The current through first diode 122 or second diode 132 isextinguished by a net voltage across capacitor 130 and the sourcevoltage appearing across the total of fault and source impedances. Thecapacitance value C of capacitor 130 may be chosen to absorb a certaindesign value of interruption current for a half cycle of the AC waveformof AC electrical source 400 with an acceptable additional voltage andalso to have enough charge stored to extinguish the fault current.

Referring to FIG. 15, a simulated source current 1500 provided to the ACcircuit breaker of FIG. 14 is shown in accordance with an illustrativeembodiment. Referring to 16, the simulated source current provided tothe AC circuit breaker of FIG. 14 zoomed to a time period when a faultcondition 1502 occurs is shown in accordance with an illustrativeembodiment. Fault condition 1502 occurred at 52 milliseconds. A breakertrip 1600 occurred at approximately 52.4 milliseconds.

Referring to FIG. 17, a power conversion system 1700 is shown inaccordance with an illustrative embodiment. Power conversion system 1700may include controller 1702, AC electrical source 400, AC electricalload 402, and one or more of semiconductor switch 100, firstsemiconductor switch 100 a, second semiconductor switch 100 b, etc.arranged in various configurations, for example, as discussed above.Controller 1702 may be electrically connected to AC electrical source400 and to AC electrical load 402 to receive voltage, current, and/orpower values used to define the parameters that control the energytransfer between AC electrical source 400 and AC electrical load 402through semiconductor switch 100, first semiconductor switch 100 a,second semiconductor switch 100 b, etc. Semiconductor switch 100, firstsemiconductor switch 100 a, second semiconductor switch 100 b, etc. arealso connected to controller 1702 that controls transmission of theon-state switching signal or the off-state switching signal to secondterminal 128 of first transistor and to fifth terminal 138 of secondtransistor 138. The voltage, current, and/or power values may bereceived for each switching frequency interval, also referred to hereinas a switching period, or may be received less frequently or morefrequently depending on the dynamic needs of power conversion system1700. Controller 1702 may dynamically control semiconductor switch 100,first semiconductor switch 100 a, second semiconductor switch 100 b,etc. to act as a 4-quadrant switch in an AC circuit breaker, in a powersharing converter, in a PWM resistive chopper, in a PWM AC buckconverter, etc. to control the supply of current between AC electricalsource 400 and AC electrical load 402 through command signals input tosemiconductor switch 100, first semiconductor switch 100 a, secondsemiconductor switch 100 b, etc.

Controller 1702 may include an input interface 1704, an output interface1706, a computer-readable medium 1708, a processor 1710, and a controlapplication 1712. Fewer, different, and additional components may beincorporated into controller 1702. For example, controller 1702 mayinclude a communication interface (not shown). The communicationinterface provides an interface for receiving and transmitting databetween devices using various protocols, transmission technologies, andmedia as understood by those skilled in the art. The communicationinterface may support communication using various transmission mediathat may be wired and/or wireless.

Input interface 1704 provides an interface for receiving informationfrom a user or from other devices for entry into controller 1702 asunderstood by those skilled in the art. Input interface 1704 mayinterface with various input technologies including, but not limited to,a keyboard, a mouse, a display, a track ball, a keypad, one or morebuttons, etc. to allow the user to enter information into controller1702 or to make selections in a user interface displayed on the display.The same interface may support both input interface 1704 and outputinterface 1706. Controller 1702 may have one or more input interfacesthat use the same or a different input interface technology. Additionalinputs through input interface 1704 may include the voltage, current,and/or power values received from AC electrical source 400 and/or ACelectrical load 402.

Output interface 1706 provides an interface for outputting informationfor review by a user of controller 1702 and for input to another device.For example, output interface 1706 may interface with various outputtechnologies including, but not limited to, the display and a printer,etc. Controller 1702 may have one or more output interfaces that use thesame or a different interface technology. Additional outputs throughoutput interface 1706 from controller 1702 may be the command signals tosemiconductor switch 100, first semiconductor switch 100 a, secondsemiconductor switch 100 b, etc.

Computer-readable medium 1708 is an electronic holding place or storagefor information so the information can be accessed by processor 1710 asunderstood by those skilled in the art. Computer-readable medium 1708can include, but is not limited to, any type of random access memory(RAM), any type of read only memory (ROM), any type of flash memory,etc. such as magnetic storage devices (e.g., hard disk, floppy disk,magnetic strips, . . . ), optical disks (e.g., compact disc (CD),digital versatile disc (DVD), . . . ), smart cards, flash memorydevices, etc. Controller 1702 may have one or more computer-readablemedia that use the same or a different memory media technology. Forexample, computer-readable medium 1708 may include different types ofcomputer-readable media that may be organized hierarchically to provideefficient access to the data stored therein as understood by a person ofskill in the art. As an example, a cache may be implemented in asmaller, faster memory that stores copies of data from the mostfrequently/recently accessed main memory locations to reduce an accesslatency. Controller 1702 also may have one or more drives that supportthe loading of a memory media such as a CD, DVD, an external hard drive,etc. One or more external hard drives further may be connected tocontroller 1702 using the communication interface.

Processor 1710 executes instructions as understood by those skilled inthe art. The instructions may be carried out by a special purposecomputer, logic circuits, or hardware circuits. Processor 1710 may beimplemented in hardware and/or firmware. Processor 1710 executes aninstruction, meaning it performs/controls the operations called for bythat instruction. The term “execution” is the process of running anapplication or the carrying out of the operation called for by aninstruction. The instructions may be written using one or moreprogramming language, scripting language, assembly language, etc.Processor 1710 operably couples with input interface 1704, with outputinterface 1706, and with computer-readable medium 1708 to receive, tosend, and to process information. Processor 1710 may retrieve a set ofinstructions from a permanent memory device and copy the instructions inan executable form to a temporary memory device that is generally someform of RAM. Controller 1702 may include a plurality of processors thatuse the same or a different processing technology.

Control application 1712 performs operations associated withimplementing some or all of the control of semiconductor switch 100,first semiconductor switch 100 a, second semiconductor switch 100 b,etc. to act as a 4-quadrant switch in an AC circuit breaker, in a powersharing converter, in a PWM resistive chopper, in a PWM AC converter,etc. The operations may be implemented using hardware, firmware,software, or any combination of these methods. Referring to the exampleembodiment of FIG. 1, control application 1712 is implemented insoftware (comprised of computer-readable and/or computer-executableinstructions) stored in computer-readable medium 1708 and accessible byprocessor 1710 for execution of the instructions that embody theoperations of control application 1712. Control application 1712 may bewritten using one or more programming languages, assembly languages,scripting languages, etc.

As used in this disclosure, the term “connect” indicates an electricalconnection whether by wire or by air or some other medium that conductsan electrical signal. The word “illustrative” is used herein to meanserving as an example, instance, or illustration. Any aspect or designdescribed herein as “illustrative” is not necessarily to be construed aspreferred or advantageous over other aspects or designs. Further, forthe purposes of this disclosure and unless otherwise specified, “a” or“an” means “one or more”. Still further, using “and” or “or” in thedetailed description is intended to include “and/or” unless specificallyindicated otherwise.

The foregoing description of illustrative embodiments of the disclosedsubject matter has been presented for purposes of illustration and ofdescription. It is not intended to be exhaustive or to limit thedisclosed subject matter to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the disclosed subjectmatter. The embodiments were chosen and described in order to explainthe principles of the disclosed subject matter and as practicalapplications of the disclosed subject matter to enable one skilled inthe art to utilize the disclosed subject matter in various embodimentsand with various modifications as suited to the particular usecontemplated.

What is claimed is:
 1. A semiconductor switch comprising: a first diodeincluding a first anode and a first cathode; a second diode including asecond anode and a second cathode; a third diode including a third anodeand a third cathode; a fourth diode including a fourth anode and afourth cathode; a first transistor including a first terminal, a secondterminal, and a third terminal; a second transistor including a fourthterminal, a fifth terminal, and a sixth terminal; and a capacitorincluding a seventh terminal and an eighth terminal, wherein the thirdanode of the third diode is connected to the third terminal of the firsttransistor and the third cathode of the third diode is connected to thefirst terminal of the first transistor and to the first anode of thefirst diode, wherein the fourth anode of the fourth diode is connectedto the third terminal of the second transistor and the fourth cathode ofthe fourth diode is connected to the first terminal of the secondtransistor and to the second anode of the second diode, wherein thefirst cathode of the first diode is connected to the second cathode ofthe second diode and to the seventh terminal of the capacitor, whereinthe third anode of the third diode is connected to the fourth anode ofthe fourth diode and to the eighth terminal of the capacitor oppositethe seventh terminal of the capacitor.
 2. The semiconductor switch ofclaim 1, wherein the first diode further includes a first controlterminal and the second diode further includes a second controlterminal, wherein the first control terminal and the second controlterminal are configured to control a state of the first diode and thesecond diode, respectively.
 3. The semiconductor switch of claim 1,wherein the first transistor is a first metal oxide semiconductor fieldeffect transistor (MOSFET) and the second transistor is a second MOSFET.4. The semiconductor switch of claim 3, wherein the first MOSFET and thesecond MOSFET are n-channel type MOSFETs.
 5. The semiconductor switch ofclaim 4, wherein the first MOSFET and the second MOSFET are enhancementmode type MOSFETs.
 6. The semiconductor switch of claim 1, wherein asource line is connected between the first anode of the first diode, thethird cathode of the third diode, and the first terminal of the firsttransistor, and a load line is connected between the second anode of thesecond diode, the fourth cathode of the fourth diode, and the firstterminal of the second transistor.
 7. The semiconductor switch of claim1, wherein the first diode has a same current rating as the seconddiode.
 8. The semiconductor switch of claim 7, wherein the third diodehas a same current rating as the fourth diode.
 9. The semiconductorswitch of claim 8, wherein the current rating of the first diode is lessthan the current rating of the third diode.
 10. The semiconductor switchof claim 1, wherein the first transistor is configured to conduct acurrent from the first terminal to the third terminal when an on-statesignal is sent to the second terminal.
 11. A power conversion systemcomprising: a semiconductor switch connected between an alternatingcurrent (AC) electrical source and an AC electrical load circuit, thesemiconductor switch comprising a first diode including a first anodeand a first cathode; a second diode including a second anode and asecond cathode; a third diode including a third anode and a thirdcathode; a fourth diode including a fourth anode and a fourth cathode; afirst transistor including a first terminal, a second terminal, and athird terminal; a second transistor including a fourth terminal, a fifthterminal, and a sixth terminal; and a capacitor including a seventhterminal and an eighth terminal, wherein the third anode of the thirddiode is connected to the third terminal of the first transistor and thethird cathode of the third diode is connected to the first terminal ofthe first transistor and to the first anode of the first diode, whereinthe fourth anode of the fourth diode is connected to the third terminalof the second transistor and the fourth cathode of the fourth diode isconnected to the first terminal of the second transistor and to thesecond anode of the second diode, wherein the first cathode of the firstdiode is connected to the second cathode of the second diode and to theseventh terminal of the capacitor, wherein the third anode of the thirddiode is connected to the fourth anode of the fourth diode and to theeighth terminal of the capacitor opposite the seventh terminal of thecapacitor.
 12. The power conversion system of claim 11, wherein aplurality of semiconductor switches are connected in series between theAC electrical source and the AC electrical load circuit, wherein thesemiconductor switch is one of the plurality of semiconductor switches.13. The power conversion system of claim 11, further comprising: asecond semiconductor switch connected between a second AC electricalsource and the AC electrical load circuit, the second semiconductorswitch comprising a fifth diode including a fifth anode and a fifthcathode; a sixth diode including a sixth anode and a sixth cathode; aseventh diode including a seventh anode and a seventh cathode; an eighthdiode including an eighth anode and an eighth cathode; a thirdtransistor including a ninth terminal, a tenth terminal, and an eleventhterminal; a fourth transistor including a twelfth terminal, a thirteenthterminal, and a fourteenth terminal; and a second capacitor including afifteenth terminal and a sixteenth terminal, wherein the seventh anodeof the seventh diode is connected to the eleventh terminal of the thirdtransistor and the seventh cathode of the seventh diode is connected tothe ninth terminal of the third transistor and to the fifth anode of thefifth diode, wherein the eighth anode of the eighth diode is connectedto the fourteenth terminal of the fourth transistor and the eighthcathode of the eighth diode is connected to the twelfth terminal of thefourth transistor and to the sixth anode of the sixth diode, wherein thefifth cathode of the fifth diode is connected to the sixth cathode ofthe sixth diode and to the fifteenth terminal of the second capacitor,wherein the seventh anode of the seventh diode is connected to theeighth anode of the eighth diode and to the sixteenth terminal of thesecond capacitor opposite the fifteenth terminal of the secondcapacitor.
 14. The power conversion system of claim 13, furthercomprising a controller configured to send a signal to switch the secondterminal of the first transistor to an on-state when the fifth terminalof the second transistor is in an off-state.
 15. The power conversionsystem of claim 14, wherein the controller is further configured to senda second signal to switch the fifth terminal of the second transistor toan on-state when the second terminal of the first transistor is in anoff-state.
 16. The power conversion system of claim 11, furthercomprising: an inductor including a ninth terminal and a tenth terminal;a second capacitor including an eleventh terminal and a twelfthterminal; and a second semiconductor switch connected between the secondAC electrical source and the ninth terminal of the inductor, the secondsemiconductor switch comprising a fifth diode including a fifth anodeand a fifth cathode; a sixth diode including a sixth anode and a sixthcathode; a seventh diode including a seventh anode and a seventhcathode; an eighth diode including an eighth anode and an eighthcathode; a third transistor including a thirteenth terminal, afourteenth terminal, and a fifteenth terminal; a fourth transistorincluding a sixteenth terminal, a seventeenth terminal, and aneighteenth terminal; and a third capacitor including a nineteenthterminal and a twentieth terminal, wherein the seventh anode of theseventh diode is connected to the fifteenth terminal of the thirdtransistor and the seventh cathode of the seventh diode is connected tothe thirteenth terminal of the third transistor and to the fifth anodeof the fifth diode, wherein the eighth anode of the eighth diode isconnected to the eighteenth terminal of the fourth transistor and theeighth cathode of the eighth diode is connected to the sixteenthterminal of the fourth transistor and to the sixth anode of the sixthdiode, wherein the fifth cathode of the fifth diode is connected to thesixth cathode of the sixth diode and to the nineteenth terminal of thethird capacitor, wherein the seventh anode of the seventh diode isconnected to the eighth anode of the eighth diode and to the twentiethterminal of the third capacitor opposite the nineteenth terminal of thethird capacitor, wherein a source connector of the semiconductor switchis connected to a load connector of the second semiconductor switch andto the ninth terminal of the inductor, wherein the second capacitor isconnected in parallel with the AC electrical load circuit and theeleventh terminal of the capacitor is connected to the tenth terminal ofthe inductor opposite the ninth terminal of the inductor, wherein asource connector of the second semiconductor switch is connected to theAC electrical source, wherein a load connector of the semiconductorswitch is connected to the twelfth terminal of the second capacitoropposite the eleventh terminal of the second capacitor.
 17. The powerconversion system of claim 11, further comprising a controllerconfigured to send a signal to switch the second terminal of the firsttransistor and the fifth terminal of the second transistor to anon-state simultaneously.
 18. The power conversion system of claim 17,wherein the controller is further configured to send a second signal toswitch the second terminal of the first transistor and the fifthterminal of the second transistor to an off-state simultaneously. 19.The power conversion system of claim 11, wherein the first diode furtherincludes a first control terminal and the second diode further includesa second control terminal, wherein the first control terminal and thesecond control terminal are configured to control a state of the firstdiode and the second diode, respectively.
 20. The power conversionsystem of claim 19, further comprising a controller configured to send asignal to switch the first control terminal of the first diode and thesecond control terminal of the second diode to an off-statesimultaneously.